[scudo] Move the blocks marking logic into markFreeBlocks()

This change is only in SizeClassAllocator32. SizeClassAllocator64 has
it implemented.

Reviewed By: cferris

Differential Revision: https://reviews.llvm.org/D158455

GitOrigin-RevId: fe0cb7b1ee0b0987cf3e01b15a2f69ed0a85d133
1 file changed